I approached plant-plant interactions with the conceptual framework of quantitative genetics, in particular Indirect Genetic Effects (IGEs). These models partition the effect that the genes have on their own bearers (direct genetic effects, DGEs) and the effect that they have on their neighbours (indirect genetic effects, IGEs). They have mostly been applied to animals and perennial plants so far. As a proof-of-concept, I first applied IGE models to the model plant species Arabidopsis thaliana, using experimental data already published by one of my supervisor (Samuel Wuest). This analysis revealed that IGEs models are able to quantify the contribution of plant-plant interaction to heritable phenotypic variation as well as to dissect their genetic architecture and evolutionary history. We notably show that alleles with positive IGE (i.e. cooperative alleles) are maintained in specific ecological habitats found at extremal latitudes in A. thaliana. This work was presented at the 2022 ESEB (European Society for Evolutionary Biology) meeting in Pragues (Poster) and published in Nature Ecology and Evolution in 2023 (see list of publication). I then applied the IGEs approach to crops, using two successive field experiments with binary mixtures of wheat varieties. This work was done in collaboration with Agroscope, the Swiss Federal Centre of Excellence in Agricultural Research. We quantified the contribution of IGEs to different agronomic traits, and identified their underlying genomic basis. We could identify some key genes with Indirect Genetic Effects, notably one of the well-known Rht genes associated with a major effect on plant height. Interestingly, we also identified one IGE locus associated with blumenol concentration, a leaf marker for AMF (Arbuscular Mycorrhizal Fungi) colonization. This result motivated a third confirmatory experiment in more controlled conditions (greenhouse) to check the association between the candidate locus and AMF colonization. This work is still on-going and involves a strong collaboration with Prof. Ian Sanders and his postdoc Erica McGale. Preliminary results have been presented to academics and plant breeders during the annual meeting of the French-speaking Cereal Breeders (mainly coming from Belgium, France, and Switzerland), and they will be published in a scientific journal as soon as the analysis of the results from the follow-up experiments is finished. Besides this work in IGEs in A. thaliana and wheat, I conducted a critical review of kin recognition studies in plants. Social evolution theories indeed predict that cooperation can also evolve when individuals are able to recognize their relatives and preferentially direct their help towards them. Multiple (controversial) studies have already reported evidence of kin recognition in different plant species, including in crops. While going through these studies, I realized that most of their results could also be interpreted as manifestations of greenbeard genes, a form of kin selection where a single gene is able to recognize similar copies of itself in other individuals. This motivated an opinion paper currently in press in New Phytologist.